As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics, which has been widely used as an energy source for various electronic products as well as various kinds of mobile devices.
Depending upon kinds of external devices in which the lithium secondary battery is used, the lithium secondary battery may be configured to have a detachable type structure in which the lithium secondary battery can be easily inserted into and removed from the external devices or to have an embedded type structure in which the lithium secondary battery is embedded in the external devices. For example, the lithium secondary battery can be inserted or removed into or from a device, such as a mobile phone or a laptop computer, as needed. On the other hand, another device, such as an MPEG Audio Layer-3 (MP3) player, requires an embedded type battery pack due to the structure or capacity thereof.
However, various kinds of combustible materials are contained in a lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to overcharge of the lithium secondary battery, overcurrent in the lithium secondary battery, or other external physical impact applied to the lithium secondary battery. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as overcharge of the lithium secondary battery or overcurrent in the lithium secondary battery, are loaded on a battery cell in a state in which the safety elements are connected to the battery cell.
Generally, the PCM is electrically connected to the battery cell via conductive nickel plates by welding or soldering. That is, nickel plates are connected to electrode tabs of the PCB by welding or soldering, and the nickel plates are connected to electrode terminals of the battery cell by welding or soldering. In this way, the PCM is connected to the battery cell to manufacture a battery pack.
It is required for the safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. To this end, a plurality of insulative mounting members or other parts is necessary, which complicates an assembly process of the battery pack. In particular, the sum of the height of the PCM and the height of the insulative cap generally reaches 3 mm with the result that a space necessary to receive the battery cell is reduced.
Meanwhile, insulative tapes are attached to respective members of the lithium secondary battery, including the PCM. In addition, a sealed portion of the battery case, in which the battery cell is mounted, is partially bent, and an insulative tape is attached to it or a barcode is printed on it. However, this process is very complicated.
Also, when external impact is applied to a battery pack, the PCM may be damaged or dimensional stability of the battery pack may be greatly lowered due to the use of the insulative tapes, which exhibit low mechanical strength.
Consequently, there is a high necessity for a technology that is capable of reducing the number of members mounted to the upper end of a battery cell to simplify an assembly process, reducing the number of welding processes to reduce a defect rate, achieving stable coupling between members loaded on the upper end of the battery cell, and increasing the capacity of the battery cell while solving the above-mentioned conventional problems.